Conventionally known among the apparatuses for measuring the length of strip-shaped tire component members such as carcass plies is the length measuring apparatus for strip-shaped rubber members. Such an apparatus measures the length of a strip-shaped rubber member, such as tread, by sequentially measuring with a one-dimensional laser sensor the gaps between the cut surfaces of the strip-shaped rubber members, which are extruded from the extruder, cut into a fixed length, and conveyed further.
The one-dimensional laser sensor emits laser light having a predetermined spot diameter of the illuminated area from a cutting slant angle direction and detects the reflected light with a light receiving means such as a photoelectric sensor. And the length measuring apparatus measures the length of the strip-shaped rubber members cut into a fixed length by calculating the gap positions, based on the principle that the intensity of reflected light weakens when the light is passed through the gap of the strip-shaped rubber members (see Patent Document 1, for instance).
It should be recognized, however, that the above-mentioned length measuring apparatus of strip-shaped rubber members cannot necessarily perform length measurement at any given position in the width direction of the strip-shaped rubber member because the displacement sensor used is a one-dimensional laser sensor.
To solve this problem, the present inventor has proposed a length measuring apparatus of strip-shaped members employing a two-dimensional displacement sensor as the displacement sensor, thereby enabling the detection of the positions of level difference in the strip-shaped member (starting end and terminating end) in a wide range of the width direction even with a single unit of displacement sensor (see Patent Document 2, for instance).
This length measuring apparatus is configured as shown in FIG. 7. More specifically, a laser light source 81a emits laser light in the form of a line. A two-dimensional displacement sensor 81 is equipped with a displacement measuring means 81b having a CCD camera that measures the amount of displacement of a tire component member 80 from a light receiving position of laser light reflected from the surface of the tire component member 80. Thus, a line beam at a predetermined angle oblique to the length direction of the tire component member 80 is emitted to the tire component member 80 that is applied around a building drum 82 rotating at a predetermined speed. At the same time, the two-dimensional displacement sensor 81 measures the positions of the starting end 80a and the terminating end 80b of the tire component member 80 by receiving the reflected light from the illuminated area.
As disclosed in the Patent Document 2, the positions of the starting end 80a and the terminating end 80b of the tire component member 80 can be measured over the whole width thereof by two units of two-dimensional displacement sensors 81, 81 which are disposed on their respective width end sides of the tire component member 80.